Question 1

How do you enable gzip/Brotli compression for HTTP responses?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express performance interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real byte counts below are **actual, measured** raw wire bytes, captured via a client that bypasses automatic decompression specifically to measure what's genuinely sent — not illustrative numbers. ## 1. Why This Even Matters — A Story First Shipping a box stuf

Question 2

What does NODE_ENV=production actually change and why does it matter?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js deployment and configuration interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the "Node core does nothing special" proof and the real Express behavior difference below were **actually run** — not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First A single word written on a sticky note ("PRODUCTION"

Question 3

What is the use of the 'os' module in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior systems-programming background assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every value below was **read directly from this real machine**, not written as a generic placeholder example. ## 1. Why This Even Matters — A Story First A moving crew arriving at an unfamiliar building first checks a few basic fact

Question 4

What is the role of the V8 JavaScript engine in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior engine-internals knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version number below was read directly from a running Node process, not quoted from memory. ## 1. Why This Even Matters — A Story First A car's engine and its dashboard, seatbelts, and cargo hold are built by different teams for dif

Question 5

How would you implement caching in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the performance-techniques question's real cache-timing proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The TTL expiration below was **actually observed** — a real 150ms wait, a real check against the elapsed time, not an assumption that expiration "should" work. ## 1. Why This Even M

Question 6

How do you manage configuration in a Node.js application for different environments?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `process.env` familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The config-switching behavior below was **actually run** across three different `NODE_ENV` values on Node v24.19.0, including the failure case. ## 1. Why This Even Matters — A Story First A single stage play script works in two different the

Question 7

What are Worker Threads in Node.js and when would you use them?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the event loop and the libuv thread pool from their own dedicated questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the blocking main-thread run and the Worker Thread run below used the **identical** computation, executed for real on Node v24.19.0 — the heartbeat contrast is mea

Question 8

Explain how the EventEmitter class works under the hood.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes familiarity with EventEmitter's public API (see the dedicated basics question), going one level deeper. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The internal `_events` inspection below was **actually run** on Node v24.19.0 — real property values, not a description of the source code. ## 1. Why This Even Matters — A

Question 9

How does `async/await` work and what are its benefits?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript interviews — assumes basic Promise familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below — including that an async function's return value really is a Promise — was **actually executed and inspected**, not assumed from how the syntax reads. ## 1. Why This Even Matters — A Story First A recipe written as "w

Question 10

Explain the differences between fork(), spawn(), and exec() in the child_process module.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `child_process` familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three functions below were **actually run** on Node v24.19.0, including a real `fork()` IPC message round-trip. ## 1. Why This Even Matters — A Story First Three ways to get help from someone in another room: shout a short instruction

NODE.JSDECODED.

Easy

How do you enable gzip/Brotli compression for HTTP responses?

What does NODE_ENV=production actually change and why does it matter?

What is the use of the 'os' module in Node.js?

What is the role of the V8 JavaScript engine in Node.js?

Medium

How would you implement caching in a Node.js application?

How do you manage configuration in a Node.js application for different environments?

What are Worker Threads in Node.js and when would you use them?

Explain how the EventEmitter class works under the hood.

How does `async/await` work and what are its benefits?

Explain the differences between fork(), spawn(), and exec() in the child_process module.

`Buffer.alloc` vs `Buffer.allocUnsafe` vs `Buffer.from` — what are the security implications?

What is the perf_hooks module and how do you measure performance?

Hard

What is `process.nextTick()` and `setImmediate()` and when to use them?

How do you profile CPU usage with --prof, 0x, or clinic.js flame graphs?

When would you use `child_process` module in Node.js?

How do you implement a circuit breaker for unreliable downstream services?

What are some common ways to improve performance in a Node.js application?

Explain the concept of 'Event Loop Pollution' and how to avoid it.

How does HTTP/2 support work in Node.js and how does it differ from HTTP/1.1?